194 Produ^ion of Ait by fuezingWater. 



Ice being perfe<rHy folid, fo that when it was melted, no air could be got from It. Tin* 

 experiment I repeated feveral times, but always found that, though the outfide of this ice 

 was perfe£tly tranfparent, and free from air bubbles^ the central parts were opaque ; and 

 though there were no diftin£t air bubbles there, yet when it was melted, a great number 

 iffued from it. The whole quantity of air, however, was not more than might have been 

 produced from the fame water in the other proceffcs in a reafonable time ; and in them 

 the producStion of air had no limit. 



Difappointed in my expeflation of getting by this means ice perfe£tly free from air 

 (which, when a large quantity of water freezes very flowly it is eafy to do, the air con. 

 tained in it retiring from that which is frozen to that which remains fluid) I diffolved ice 

 that was perfe£lly tranfparent, and therefore free from air, in veffels containing mercury, 

 and expofed it to froft a fecond time. But I always found that when the whole of it was 

 frozen, the extreme parts were tranfparent, the central pirts were opaque, and when dif- 

 folved, yielded air. Though I repeated this procefs ten t>r a dozen times with the fame water, 

 always letting out the air that was procured by freezing, prefently after it was extricated, 

 and before it could have been re-abforbed ; yet on expofing it tc another freezing, I never 

 failed to get more air, and the harder the froft was, the more air 1 procured. 



As there is an evaporation from ice no lefs than from wateri the interftices made by the 

 cryftalization of the water, when it is converted into ice, will fbon be filled with vapour -y 

 and this vapour, like that which is formed by heat, becomes tix baHs, I fuppofe, of a 

 quantity of air. Since, however, the mod tranfparent ice fwims in water, this alfo mull 

 have interftices, but they contain no air ; being fuch as exift in the moft folid bcdies in 

 which (gold itfelf not excepted) the component particles are not in perfe£l contaft, fince 

 they are reduced into lefs dimenfions by cold. 



As the veffels I made ufe of in thefe experiments were either cylindrical jars, or 

 conical wine glaffes, and, confequently, the bubbles of air procured by freezing were 

 expofed to a confiderable furface of water, and would in time (though not, I found, in the 

 courfe of a day) have been abforbed by the water more free from air, I procured glafs 

 veffels of a conical form, terminating in narrow tubes, into which the air diflodged from 

 the ice might afcend, and not be fubje£t to be abforbed. I was fo fortunate as to have 

 feveral veffels of this form, and they completely anfwered my purpofe for five or 

 fix proceffes. 



Thefe veffels were firft filled with mercury, and then 1 introduced into them a quantity 

 of water freed from air by previous freezing ; and when, after expofure to froft the ice 

 was melted, the air diflodged from the ice afcended into the narrow tubes, and remained 

 without any fenfible diminution of bulk feveral days ; and every time that the water was 

 expofed to the froft, an addition was made to it. At length, however, though the veffels 

 were very ftrong, and contained much mercury, which, by its tendency to defcend, would 

 give the water room to expand with the lefs danger of breaking the veffel, none of them 

 ferved for more than the number of proceffes above-mentioned. 



After 



